Chief Executive John Lee on Friday told officials to replace a steel water pipe lined with bitumen where black particles found in tap water at two housing estates in Fanling likely came from.

He also asked officials to form an expert group to look into freshwater supply at Queen's Hill Estate and Shan Lai Court, while Secretary for Development Bernadette Linn will lead a team of Water Supplies Department staff to the area for investigation on Saturday.

"The incident must be dealt with promptly, to completely eliminate residents' concerns and ensure the water supply is safe," Lee wrote on social media, following a high-level government meeting on the matter in the afternoon.

He said the priority is to replace a 400-metre-long steel water pipe in an upstream area, where the authorities believed the bitumen came from flaking of the coating.

"The Development Bureau has to instruct the Water Supplies Department to conduct a risk-based review to determine whether other areas require the installation of filters, and to propose a long-term plan on replacing water pipes," Lee added.

Other key tasks set out by the CE included inspecting the filtration system at the two estates twice a day, cleaning the water tanks at all the blocks, unveiling testing results of water samples daily, and reaching out to residents to see if they need assistance.

Deputy Financial Secretary Michael Wong has been appointed by Lee to oversee such works.